This is a continuing study of the constitution, mechanisms, and properties of amalgams. Early compressive flow measurements will be compared with setting expansion and mercury absorption results for a series of silver-tin, and silver-tin-copper amalgams. The data will be used to test the hypothesized correlation of dimensional change with a solid-solid reaction rather than with direct mercury reaction. Metallography, microprobe analysis, and xray diffraction will be used to characterize the microstructures produced in amalgams containing two types of alloy particles (silver-tin and copper bearing). Effectiveness in suppressing gamma-two phase formation will be evaluated relative to copper content, activity and distribution.